Add ability to disable tools

[satur9nine]

No description provided.

[Ebola-Chan-bot]

这个设计在与已有的环境变量重命名机制共存条件下就显得太臃肿了。建议改成，要禁用一个工具，就将其对应环境变量设为非法值或保留关键字，如"<disabled>""null"，之类的，避免任何容易出错的名称问题，也不需要再增添新的环境变量。
不过在“只希望允许个别工具”的场景下，新增一个环境变量可能确实让配置更简洁。值得讨论。 @Aas-ee

不一定需要修改，先讨论一下

[satur9nine]

Your feedback is appreciated, I have updated the change to use the sentinel string "null" or "<disabled>" to disable the tool.

[Ebola-Chan-bot]

After discussions with other maintainers, we decided to allow only <disabled> as the tool disable flag, and not to include the ambiguous null or other invalid names. In other words, tool disabling is only indicated when and only when the tool name is precisely set to <disabled>, the reserved keyword; other illegal names should only be warned and fallbacked to standard names, instead of disabling that tool.
Also better if provide examples in the README.

[satur9nine]

After discussions with other maintainers, we decided to allow only <disabled> as the tool disable flag, and not to include the ambiguous null or other invalid names. In other words, tool disabling is only indicated when and only when the tool name is precisely set to <disabled>, the reserved keyword; other illegal names should only be warned and fallbacked to standard names, instead of disabling that tool. Also better if provide examples in the README.

OK excellent, I've updated the PR with your suggested changes.

[Ebola-Chan-bot]

The new configuration examples:

# Disable search tool
MCP_TOOL_SEARCH_NAME=<disabled> npx open-websearch@latest

do not work in bash/zsh. < and > are parsed as input/output redirection, so the shell attempts to read from a file named disabled and fails with bash: disabled: No such file or directory (or silently corrupts the command).

Since the sentinel value itself contains shell-special characters, the docs must show the quoted form:

# Disable search tool
MCP_TOOL_SEARCH_NAME='<disabled>' npx open-websearch@latest

Also add a note that on Windows cmd, double quotes are required (MCP_TOOL_SEARCH_NAME="<disabled>"). The table description should likewise mention quoting when the value is used in a shell environment.

[satur9nine]

The new configuration examples:

# Disable search tool
MCP_TOOL_SEARCH_NAME=<disabled> npx open-websearch@latest

do not work in bash/zsh. < and > are parsed as input/output redirection, so the shell attempts to read from a file named disabled and fails with bash: disabled: No such file or directory (or silently corrupts the command).

Since the sentinel value itself contains shell-special characters, the docs must show the quoted form:

# Disable search tool
MCP_TOOL_SEARCH_NAME='<disabled>' npx open-websearch@latest

Also add a note that on Windows cmd, double quotes are required (MCP_TOOL_SEARCH_NAME="<disabled>"). The table description should likewise mention quoting when the value is used in a shell environment.

Valid point, I have updated this PR to include these details in the two README files.